Lithium-ion battery charge control method

Abstract

A technique of operating a lithium-ion (Li-ion) battery is proposed for maximizing battery life. In a first instance, this technique calls for charging the battery at a lower temperature than the temperature at which discharge begins. Preferably, the battery is charged at a temperature T 1 in the range between about +5° C. and -20° C.; and discharged at a temperature T 2 , in the range of about +5° C. to +30° C., T 2 being higher than T 1 . In another instance proposed by the invention, the battery is charged to an elevated state of charge which is above an initial state of charge at a temperature T 1 between about +5° C. and -20° C. which is lower than a temperature T 2 , in the range of about +5° C. to +30° C., at which discharge begins. In still another instance proposed by the invention, after the battery has been charged and discharged during the eclipse season, it is then charged to an intermediate charge level between about 40% and about 60% state of charge over a relatively long lapsed duration of time, about one month to about six months, and thereafter, the battery is maintained at this intermediate charge level.

What is claimed is: 
     
       1. A method of operating a lithium-ion (Li-ion) battery so as to maximize battery life comprising the step of: (a) charging the battery at a lower temperature than the temperature at which discharge begins.   
     
     
       2. The method of operating a lithium-ion (Li-ion) battery as set forth in claim 1 wherein step (a) includes the steps of: (b)charging the battery at a temperature T 1  in the range between about +5° C. and -20° C.; and   (c) discharging the battery at a temperature T 2 , in the range of about +5° C. to +30° C., which is higher than T 1 .     
     
     
       3. The method of operating a lithium-ion (Li-ion) battery as set forth in claim 2 including the step, prior to performing step (c), of: (d) heating the battery prior to the onset of step (c).   
     
     
       4. The method of operating a lithium-ion (Li-ion) battery as set forth in claim 2 including the step, prior to performing step (c), of: (d) heating the battery to the temperature T 2  prior to the onset of step (c).   
     
     
       5. A method of operating a lithium-ion (Li-ion) battery so as to maximize battery life, the battery being less than fully charged, the method comprising the step of: (a) reaching an elevated state of charge above a minimal state of charge at a temperature T 1  between about +5° C. and -20° C. which is lower than a temperature T 2 , in the range of about +5° C. to +30° C. at which discharge begins.   
     
     
       6. A method of operating a lithium-ion (Li-ion) battery so as to maximize battery life, the battery being initially substantially discharged, the method comprising the step of: (a) partially charging the battery to a charge level between about 40% and about 60% state of charge; and   (b) maintaining the battery at the charge level of step (a) for a relatively long elapsed duration of time.   
     
     
       7. A method of operating a lithium-ion (Li-ion) battery as set forth in claim 6 (a) partially charging the battery to a charge level between about 40% and about 60% state of charge; and   (b) maintaining the battery at the charge level of step (a) for the duration of the solstice season between successive eclipse seasons.   
     
     
       8. A method of operating a lithium-ion (Li-ion) battery as set forth in claim 6 wherein the relatively long lapsed duration of time of step (a) is in the range of about one month to about six months.   
     
     
       9. A method of operating a lithium-ion (Li-ion) battery as set forth in claim 6 wherein the relatively long lapsed duration of time of step (a) occurs twice a year.   
     
     
       10. A method of operating a lithium-ion (Li-ion) battery as set forth in claim 6 wherein the battery is a component on a spacecraft; and   wherein the charge level is of sufficient magnitude to provide adequate energy to support the spacecraft if a spacecraft upset occurs.